Individual carbon nanotubes (CNTs) are at least one order of magnitude stronger than any other known material. CNTs with perfect atomic structures have a theoretical strength of about 300 GPa. In practice carbon nanotubes do not have perfect structures. However, CNTs that have been prepared have a measured strength of up to about 150 GPa, and the strength may improve upon annealing. For comparison, Kevlar fibers currently used in bullet-proof vests have a strength of only about 3 GPa, and carbon fibers used for making space shuttles and other aerospace structures have strengths of only about 2-5 GPa.
CNTs prepared according to present methods are far too short to make effective use of their strength and/or cannot be prepared in sufficiently large quantities.
CNT fibers can be drawn from CNT-polymer solutions or directly from CNT arrays. However, due to practical difficulties in dispersing, assembling and aligning carbon nanotubes using a CNT-polymer route, a strategy based on direct spinning of fibers from CNT arrays is more attractive.
The spinnability of CNT arrays depends greatly on the quality of the arrays, including CNT alignment, density, purity, length, and other factors. CNT arrays of the prior art are generally not good precursors for fibers because they tend to be contaminated with amorphous carbon. Too much amorphous carbon tends to affect the spinnability of the CNT arrays in a deleterious manner.